how to measure transom height for outboard motor

Boaters who consider going with a higher mount can see increased speeds. A long shaft engine requires a height of 20 and extra-long shaft engines will need a transom height of 25. The standard installation of an outboard has the top of the transom of the boat at the same level as the bottom of the motor portion of the outboard. Well, raising the outboard motor can be an easy task for you. Determining Your Boat Transom Angle The transom angle - commonly measured in degrees - is the transom's vertical inclination. Outboard shaft length plays a crucial role in the performance of your boat. The flat part of the bracket that rests on the transom when mounted will give you the same point of reference as the transom does on the boat. With some boats I have a pretty good idea as to what length motor should be hung on them. disregard the downward pointing "hooks" at the front of the For vee-shaped hulls, the lowest spot of the hull will come to point, while on flat-bottomed boats it will be more or less level. It is extremely important that the boater understands the significance of the transoms height. You must be still in the blue about that matter. Buying a boat can be an exciting purchase. The pros and cons of properly . This provides seaworthiness and offers maximum protection from large seas. motor brackets Now that you have a better understanding of boat transom heights its time to take out the ruler and get the perfect measurements. and I'll explain it better, (or point you to someone that can help. Outboards designed for saltwater applications usually have longer shafts. The rearmost structural member of your boat, it not only distributes the stress of the hull generated by the bow's impact as it cleaves the water, it's the place you hang your outboard motor. When the boat transom is too low, the motor could end up underwater. 7. Before we get started lets see what a boat transom is and what it does. Then open up the clamp bucket. Learn More About Your Boats Systems By Joining The Born Again Boating Academy! This measurement is primarily designed for single motor propulsion. It also cuts into speed and fuel efficiency. It also includes attaching the right engine. Tilt your motor until the bullet of the gearcase is With more than a decade of experience cruising the lakes in my Crestliner Grand Cayman pontoon boat and my Boston Whaler, I now want to share everything I've learned with my community here at Boating Hub. This email address is being protected from spambots. This will ensure the best performance. trimming the motor out by one-half to full trim. Each one has a totally different effect on the boats performance. You dont have to be a mathematician to determine the correct boat transom angle. 2019s List of the Best Recreational Pontoon Boats for Sale. Anything bigger than that your obviously going to need an extra long shaft. clearInterval(interval); Measure from the top of the transom to the bottom of the hull. If you are running a twin-engine setup, then measure the same distance from each clamping plate to the bottom of the hull. Top 10 Choices for Boaters, Mercury Introduces 600HP V12 Verado Outboard Engine, The Outboard Expert: Tohatsu Propane Outboard Engine. Other uncategorized cookies are those that are being analyzed and have not been classified into a category as yet. If your boats transom height is 15-16, a short shaft engine is required, and if it is 20-21, a long shaft engine is required. The current measurement is the ventilation plate is about 1 1/2" above the true keel line which is about 24" in front of the motor edge. Before we start measuring the outboard shaft length, lets get it clear about whats referring to when we talk about the outboard shaft length. Boats with more engine power and weight require longer shaft outboards for better balance. However, youll notice a little increase in drag and a decrease in top-end performance. If so, send me an The height of the boat transom dictates the size of the outboard motor. The dealer just hit you with the long or short shaft question and you have no clue as to what you need or even what he's talking about. It is possible that the motor could hang low while transporting on the boat trailer causing future boat repairs. Will Charpentier is a writer who specializes in boating and maritime subjects. All you need to do is measure how much to rise. bassboat can be a bit confusing at times; hopefully this will help sort Your at your local outboard dealer shopping for a new motor and the salesman hits you with the question, "short or long shaft?". would be more accurate.) Actually there is no designated letter for short shaft. Sluggish speeds, poor handling, heavy spray, porpoising, or even water pushing up into the cowling are all signs that an outboard is set too low. 1 0 obj With the motor trimmed so that the propshaft is parallel to the keel, the anti-ventilation plate should be just about even with your straight edge, and thus even with the boat bottom at the keel. "brackets". Mounting the motor lower on the boat transomcan createexcessive spray, increase case drag, reduce underwater clearance, and negatively impact faster boats. mpeSelector: ".pt-mpe", If your boat is newer and the manufacturer is still in business, you might also want to try to give them a call. This cookie is set by GDPR Cookie Consent plugin. Simply start with the engine in idle, followed by, If you decide to make some custom adjustments we have the. debugMode: false, A: The answer varies by boat, but here are some rules of thumb for matching a short shaft outboard to your boat. Height Measurement: Recommended Shaft Length: 14" - 17.25" 15" Shaft (Short) 17.25" - 19.5" Varies by application 19.5" - 22.5" As you can see, the measurement is about 2 1/2". A reversetransom that sits too high can impact the propellers of the motor and motor bracket. Extra-extra long shafts are 30-inches long. On this type of boat, if you are in doubt, default to the longer-shafted outboard. The brackets can add 1 inch to the overall mounting height of the outboard. A: Any boat that has a 21 to 27 inch aft transom will need an extra long shaft outboard. Each one has a totally different effect on the boats performance. Boat Transom Heights The Beginners Guide, Buying a boat can be an exciting purchase. endobj With a jack plate, you can mount it exactly where you want it. Your goal is to measure how the outboard will sit, so start from the clamping plate and follow the centerline of the hull. You need JavaScript enabled to view it. Many boat transoms are modified to use a different length of outboard by using a bracket. Before we get started lets see what a boat transom is and what it does. What matters is the actual measurement in the specifications, not the name. To achieve 35 mph with a 6 hp engine, the total weight is 135 lbs (boat motor fuel passengers). The first order of business is to measure your boat for the ideal fit. However, with the outboard shaft length too short, meaning the prop is too close to the surface, the engine is likely to ventilate and therefore slip on acceleration or lose power. It was a 23-foot Crestliner Grand Cayman pontoon boat. The clamp bracket on the latest Mercury Four-Stoke-model outboards has five mounting bolt holes spaced .75 inches apart. <> The cookie is used to store the user consent for the cookies in the category "Other. xmlHttp.send('{"store_id":"369079","timezone_offset":"-5","timestamp":"2023-03-04T05:39:31.71020200Z","visit_id":"e2642be3-34e5-4a48-b89d-639d139834e0","channel_id":1}'); <>/Metadata 127 0 R/ViewerPreferences 128 0 R>> mpeInit(); (updated Shaft lengths are available in increments of 5. If the propeller fails to ventilate, the motor is mounted to low. I mean, who wants to purchase something as expensive as an outboard to only realize you bought the wrong one. from the transom. How the outboard will sit on the back of the boat depends on how the transom is designed. Step 2 requires the propeller's radius (check the user manual and then the technical drawing). When mounting the engine, you want the cavitation plate to be 1 above the boat bottom for every 12 away from the transom. For really big boats, the biggest and baddest six- or eight-cylinder outboards can have extra-extra long shafts up to 30 inches. The standard shaft length for most outboard engines less than 125 horsepower is 20 inches. For most boaters this is a no brainer, but for the novice or inexperienced boater it may be a tougher question. s.setAttribute("rel", "stylesheet"); Set the end of the tape on the outside edge of the taffrail at the center and measure inward to the inside edge of the taffrail. Figuring out how to measure motor height on a center of the propshaft. Actual shaft length is 21.5" on those. So you should just measure the height of the boats transom from the center down to the lowest point of the hull, and compare transom height with the outboard shaft length numbers. Finding the right size is a matter of looking at what youve got and taking out the measuring tape. With the outboard shaft length too long, meaning the prop is too deep in the water, the engine wont be as efficient, and the fuel burn is high. The transom is the "back wall" of your boat, the most rearward part of your hull. If your outboard motor height. ), Al Shields I would ask you to go back and measure the transom of your boat. Generally, the anti-ventilation plate on most engines is aligned with the bottom of the vessel. maxTerm: 36, Wherever the outboard clamping bracket is, use this as the basis for measurement. Rebuilt - What You Need to Know, Lower Unit and Sterndrive Break-In Instructions. d.addEventListener("DOMContentLoaded", function (e) { Workboats, sailboats, and displacement-hulled boats fall into this category. (Any measurement given as "off the transom" If you have a fast boat, getting the outboards cavitation plate at the same level of the hull will ensure quick hole shot and fast top-end speeds. You reply, "Im not sure, I think its a long". Read the measurement on the transoms bottom. This measurement would be the inches of I mean it is better to be safe than sorry, am I right? You can use a longer shaft than recommended and your boat will work fine. The height is approximately six inches higher than with a propeller. Save my name, email, and website in this browser for the next time I comment. As mentioned above, the operation of the propeller relies on the transom height. } This would not be a good thing. Be sure to measure carefully and research thoroughly before diving in. What Kind of Fuel Does Your Marine Engine Need? I show you how to consistently measure your prop to pad height. Setting Height of Outboard Motor - YouTube 0:00 / 0:46 Setting Height of Outboard Motor nates90 71 subscribers Subscribe 83 Share 63K views 7 years ago #boatservice #outboardmotor. If it measures between 17 and 22, you'll want to go with a long shaft motor. To measure your outboard motor shaft length, measure from the bottom of the mounting bracket where it rests on the transom to the top of the cavitation plate, this is the horizontal surface of the lower unit immediately above the propeller. Higher mounting decisions should be left to the professionals. August 9/08). The first step is to determine the height of your boat's transom. This was the height of my 225 Yamaha on my TR21 The height of the transom is estimated by using the center line to measure from the bottom of the hull to the top of the transom. (function () { There are a series of four to six holes at the top of the bracket, and the lower bolts actually fit into slots. If youre going the other way around and trying to figure out how long the shaft on your outboard is, measuring it is equally easy. The outboard shaft length is the vertical distance between the top of the mounting clamp bracket and the bottom of the cavitation plate (aka the ventilation plate). a Detwiler manual jackplate. If your boat planes, pay extra attention to getting the shaft length as close to perfect as possible. Boats that use longer outboard shafts include: And the rule of thumb is that you should keep the cavitation plate level with the bottom or keel of the boat. Take your time and understand your boat and your entire transom. I live for the weekends when I can go out on the water and escape the stress of life on land. What types of boat need an extra long shaft? var h = d.getElementsByTagName("head"), This distance is very important to the performance of you boat. s.setAttribute("type", "text/javascript"); bracket. MarinePartsMan.com also says that V6 bass-boat engines have a 20-inch shaft. In the case of a larger offshore boat, it may be to the top of a cutout on the . A1: Broadly speaking, the outboard motor shaft length for pontoon boat, bass boat, or other larger boats should be long shaft. If you are looking to repower, they may be able to offer some sage advice. Move the bracket as close to the center of the transom as possible while still maintaining clearance to allow the main outboard or rudder to reach its full range of motion without contacting the kicker motor. You can find your Mercury outboard model code on an ID plate or sticker. This restriction includes most fishing boats and longer sailboats. These cookies help provide information on metrics the number of visitors, bounce rate, traffic source, etc. Increased RPM and additional horsepower feed the need for speed. This is handy if youre shopping for second-hand outboards or looking to sell the one that came with your boat. In step 3, add another 10 cm (4") to the previous calculation in order to develop the ideal shaft length. We use cookies on our website to give you the most relevant experience by remembering your preferences and repeat visits. If we run into that scenario, I would still show you the different options of motors and go over pricing, but I would also ask you to hold off and do one thing before you pull the trigger. No one wants to have issues with a new transom or boat repairs. Triton. Increased RPM and additional horsepower feed the need for speed. Another important measurement is the transom angle. Place the bracket on the transom to the left of the main outboard or rudder. hulls, such as Allisons, Bullets, Strokers, etc., this measurement could })(); Smaller 12-14 foot boats can require either a short or long shaft outboard depending on the style of the boat and the brand. Ten years ago I bought my first boat. The transom is the flat vertical section at the rear of the boat. (Putting a Allowing the propeller to pull water from underneath and push it out behind the boat. Higher mounting decisions should be left to the professionals. Where Onboard a Boat is the Transom Located and More About Transom Heights A propeller operates based on the height of the transom. Because of the increased friction, cavitation reduces efficiency. The engine may be lifted one inch for every eight to ten inches of distance between the transom and the prop, according to a boat riggers rule of thumb. It does not store any personal data. So if you are measuring the outboard shaft length for smaller boats, inflatables, dinghies, sailboat or other low-speed work boats, the cavitation plate is often about 2 below the bottom. }, 100); It also cuts into speed and fuel efficiency. One of the main concerns is causing the engine to overheat if not enough water reaches the engine to keep it cool. the propshaft below or above the pad. loadScript(ptScript); While this is the case there is certain saltwater motors that are extra extra long at 30. Youll also want to pay attention when youre in shallow water because your prop will be lower than normal. The how to measure the shaft length of an outboard motor is a question that many people have asked. The lowest point will likely be directly under your drain plug if youve got one. No one wants to have issues with a new transom or boat repairs. h[0].appendChild(s); The transom in a boat today is a place to hang your outboard motor. All rights reserved. resting on the transom if you had the motor all the way down on the boat Take the center measurement from the top to the bottom of the hull. Knowing how this can affect the overall operation of the boat is a factor to be considered. You may wonder how deep your prop should be in the water. Lastly, knowing the year of your motor and what style of controls you have (side mount, concealed side mount, or binnacle) is also a plus because it will tell the dealer if your current controls are compatible with the motor you are purchasing. To do so, you will want to measure at the exact center of the transom from the very top to the very bottom. The most common percent angle is probably 12, however spec sheets for O/B and I/O boats may show 10 percent, 12 percent, and 14 degrees. var interval = setInterval(function () { If you decide to make adjustments, please consult a marine engine dealer about the boatdesign. My family and I used it to fish, ski (yes, you can ski behind a pontoon boat), and cruise the lakes near our home. (In the case of the faster Cutting the transom down is the only legal method to utilize a short shaft engine on a tall transom. If you go too short your more than likely going to cavitate and loose power. Read the following to get the optimal shaft length for outboard motors! The motor length corresponds to the transom height of the boat, measured from the keel to gunwale at the transom. This also means it can affect the safety of the boat. To make the yard stick long enough to measure the length of all the clubs, tape the ruler to the top. With the long side (22 1/2), place a carpenters square ) in opposition to the keel. Or measure from the main engine prop up to the water line? When fighting waves from the stern, a 20-inch transom is considerably safer. Industry transom height standards have been evolved during the last 30 years: 15 for short shaft engines, 20 for long shaft engines, and 25 for extra-long shaft engines. Out of these, the cookies that are categorized as necessary are stored on your browser as they are essential for the working of basic functionalities of the website. But in many cases, its a little more complicated than that alone. Small portable outboards ranging from 2 to 20 horsepower are usually sold only in short or long shaft versions. Another important measurement is the transom angle. These are vertically aligned so the boater can make adjustments. This allows the engine to idle without the flow of the exhaust being restricted. Chances are the boat was designed with a specific size of outboard in mind. There are also specialty motor shaft lengths. | Sitemap, The Marine Parts Warehouse Outboard Museum, OBR Powerhead / Shortblock Warranty Claim Form, Remanufactured vs. But opting out of some of these cookies may affect your browsing experience. How Transom Height Is Measured This will be the ), and place it on the bottom of the pad in the center. Since the length of the shaft of your outboard is associated with the size boat, smaller engines will generally have shorter shafts. Some fishing boats can handle the motor being underwater. The outboard comes with mounting holes and brackets. This is also known as the shaft length. It can also improve the experience of driving a faster boat. Plus, a low transom cut is an invitation for the water to flood the boat. var addy_textd53b59933f6c3f2e8b59f1b4a6d41fa5 = 'info' + '@' + 'vanssports' + '.' + 'com';document.getElementById('cloakd53b59933f6c3f2e8b59f1b4a6d41fa5').innerHTML += ''+addy_textd53b59933f6c3f2e8b59f1b4a6d41fa5+'<\/a>'; gtag('config', 'G-QX0Y76NH40'); Whether your on a pontoon boat, fishing boat, or speedboat boating is always one of the best times you can have. Long shafts are 20-inches long. A deep Vee hull will result in a different measurement than a flatter . var ptScript = "https://cdn.paytomorrow.com/js/pt-mpe.min.js"; Among them will be first-timers or those who have recently purchased their boats. Keep these numbers in mind if you ever have a need for a new outboard motor for your boat. When trimming your motor, they provide you a greater bow response. Repowering your boat is one of the most expensive upgrades you can make. Using your existing control box and gauges will save you quite a bit of money in the end. So how to measure outboard shaft length? However, the motor should not be raised more than 5 inches above the standard position. window.dataLayer = window.dataLayer || []; Functional cookies help to perform certain functionalities like sharing the content of the website on social media platforms, collect feedbacks, and other third-party features. As with anything, there are exceptions to the rule. If you have an outboard motor, the distance from one end to another will be found on the side or on a label near its bottom. To do so, take a measurement from the very top to the very bottom of the transom in the precise center. up to the bottom of the motor brackets, (as in #1). The boat transom can be flat with zero degree angles. If you said you have a pontoon or a larger style boat such as a bass boat or speed boat, I would be pretty confident in saying it needs a long shaft. Other factors to consider when determining the mounting height of an outboard are related to performance. Place the clubs bottom on the ground as though it were going to be used to strike a golf ball. It will ensure that the outboards trim will be effective, and it will save you gas too. If it measures anywhere from 17" to around 22", then your going to want to go with a long shaft motor. A2: Instead of changing to the short outboard shaft, you can try the Jack Plate first. Keep these numbers in mind if you ever have a need for a new outboard motor for your boat. Keep these numbers in mind if you ever have a need for a new outboard motor for your boat. Then finally test your outboard, if the mount is perfect. This illustration depicts four different outboard mounting height options (courtesy Mercury Marine). In the case of a dinghy or johnboat, this point may be the top of the transom. PayTomorrow.mpeInit({ Spark Plug 25.0nm(18.4 Ft-lb) (2.55 Kgf-m) Necessary cookies are absolutely essential for the website to function properly. s = d.createElement("script"); Check the literature about your model boat online, and you may be surprised to find that the number is published for you. Safely but briskly accelerate. document.getElementById('cloakd53b59933f6c3f2e8b59f1b4a6d41fa5').innerHTML = ''; This is a measurement that has been used for BassCats, I'm According to MarinePartsMan.com, the outboard can be raised 1 inch above the standard height for every 10 miles per hour of speed the boat can attain. There Beginning boaters should be aware of the boats measurements. Step 3: Add another 10 cm (4'') to the previous calculation for the final ideal shaft length. The height of the transom is calculated by measuring from the bottom of the hull to the top of the transom, using the center line. Gear case sits just below or at the hull depth due to the deep v. A long shaft engine requires a height of 20 and extra-long shaft engines will need a transom height of 25. h[0].appendChild(s); He is also a certified marine technician and the author of a popular text on writing local history. The clamp bracket is designed so that the engine's mounting height on the transom can be adjusted higher than standard. They operate as a planing surface, allowing your boat to climb to the top more quickly. Again, make sure that you are measuring to the flat part of the brackets; Doing this can have adverse effects. This is measured by the propeller shaft being parallel to the vessels bottom. s.setAttribute("src", script); straight edge on the top of the transom to "extend" it out parallel with the straight edge. priceSelector: ".price--withoutTax, span.price.price--withTax", How can you figure out what your transom angle is? manufacturer will recommend the outboard height according to the bracket shape and length. On the downside, a higher mount can interfere with the boaters steering capabilities. Mounting the outboard a little bit lower than the standard point could avoid the possible ventilation and slip on acceleration. What is the Virtual Sundance Film Festival? To sum up, there is a simple calculator of the shaft length for outboard motors: Outboard Shaft Length = Transom Height +/- Factors. Simply start with the engine in idle, followed bytrimming the motor out by one-half to full trim. You need JavaScript enabled to view it. var BCData = {"csrf_token":"d7ecb6b56891bb66aee12dbc01a80162b3ed582c1acbe30f16fc9f1b2abc362f"}; height (that I'm aware of); probably the most common is: The motor is what powers the boat so the two go hand-in-hand. Since the ventilation plate & foil are burried under water it is obviously too low. var xmlHttp = new XMLHttpRequest(); Transom Outboard Engine Position - YouTube 0:00 / 0:56 Transom Outboard Engine Position BOATING SCENE 763 subscribers 609 211K views 5 years ago www.boatingscene.com.au Sometimes when your. You run the risk of possibly unsafe handling if you attempt to put a long shaft engine on a transom designed for a short shaft engine. The Effects of Standard, Lower and Higher Mounting. #1: Height will be to the flat part; if you measure to the bottom of the brackets

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